'Ordinary' film

I am wanting to make a neg with 'ordinary' film and therefore need to convert from pan sensitivity. Although I suspect it may not be possible to make a true reproduction would it be a simple matter of using a blue filter? If that is the case is there any particular type or colour of blue filter or are all 'blues' the same? Would the Cokin type be suitable and what density? Density may only have effect on exposure time - but I don't know.
Any suggestions?

Thanks for the reply.
The thing is I want to try to replicate the very early photographs which were photographed with film only sensitive to blue light. In the early days, once ortho had been invented, this film was referred to as 'ordinary' film. Hence my interest in wanting to revert to blue only sensitivity.
Size-wise I use 5x4 and 5x7.

would paper negatives work for you ?
they are orthochromatic, and slow and like olde filme .. sort of.
since you are shooting large format its easy ... ( and maybe already in your darkroom ).

you could also coat your own ( i like doing that these days ) with liquid emulsion
and regular paper, or glass. the only thing about the glass is you need plate holders
and it takes practice coating it ... paper is a piece of cake ...

Paper negs?? Good call, trouble is I don't have a darkroom. I have given thought to paper negs before, simply to try them, but got no further. No darkroom?so what do I do? - Salt prints, I can get away with a large Harrison tent thing for loading and then dev in a Paterson 10x8 colour processor and subdued light for coating. Although I'd really like to give paper negs a try, I might get as far as getting a negative but printing would be the next problem. I don't know how they would work for salt prints and only UV light.
So, as much as I definitely like salt prints, they are really the only printing I do (other than those other unmentioned type). So I'm back to the blue filter situation.

bummer, no darkroom ..
can you get a safelight red-bulb, and replace a room light with it ?
i do that on occasion, it works OK ...
...once you have the image you could get a hot plate and paper towel, cloth (to protect the paper)
and some bees wax or parafin and translucentize your negative.

the original salt prints were done on paper negatives, people have been waxing paper
negatives since around the same time ...
it might be something to think about if the blue filter doesn't work

if you coat your own with liquid emulsion it is pretty slow ..
i use butcher paper for my paper negatives, it is plentiful and CHEAP ( and THIN ) ...
can't say how archival it is though ...

I do a fair amount of optics system design at work for medical devices so forgive me for the more complicated answer than any sane (non-geek) person would actually want

Well, a blue filter would get you part way there. For a given process, there is a graph that describes the sensitivity as a function of wavelength. Here is an example provided by Joe Smigel for wet plate with different proportions of iodide vs bromide salts. Now, compare that to a 80A Hoya filter. As you can see, the spectral transmission graph of an 80A blue filter shows a peak transmission around 440 nm and still lets some red light through all the way into the far red while an iodide emulsion has a peak out to 420 and completely insensivity at 440 and beyone. What does all this mean? It means that a blue camera filter will only get you part way there, but it may be far enough for the look you want. To really mimic the spectral characteristics you'd need a bandpass filter like those at Edmund optics.....the off the shelf filters tend to be small and very pricey.